This invention relates to a cathode coating dispersion containing graphite and/or carbon black and a resin epoxy which is suitable for use in batteries, fuel cells or capacitors.
Alkali battery dry cells are manufactured by pre-forming a steel can and then nickel plating the inside of the can. Molded rings made from the cathode materials, generally containing a mixture of manganese dioxide, graphite and potassium hydroxide, are tightly fitted inside the can. The inside of the can is treated with a conductive dispersion which is placed between the inside surface of the can and the molded rings in order to improve the electrical contact between the can and the rings and to prevent corrosion of the nickel layer and the can.
Various emulsions have been utilized in an attempt to maximize electrical contact and prevent corrosion in batteries. These emulsions generally contain graphite and/or carbon black in combination with a binder. For example, U.S. Pat. No. 4,810,600 utilizes a dispersion containing graphite and/or carbon black in combination with a binder of a) vinyl acetate and ethylene, b) vinyl acetate and vinyl chloride, c) styrene and butadiene, or d) vinyl acetate, vinyl chloride and ethylene. In addition, other dispersions have been utilized containing binders of aromatic polyurethane, styrene acrylic, aliphatic polyester polyurethane, vinyl acetate acrylic, aliphatic polycarbonate urethane and fluoropolymer. All of these various dispersions exhibited some form of failure when subjected to high concentrations of potassium hydroxide. The dispersions all showed high resistance after the KOH test as opposed to before the test and in some cases the binders either became soft or lost adhesion when sprayed on the nickel plated panel, dried at 80xc2x0 C. for 20 minutes and then immersed in 40% KOH solution for 72 hours at 80xc2x0 C.
Accordingly, it is an objective of the present invention to provide a graphite-containing cathode dispersion for batteries which will improve the storage and discharge properties and form an electrically conductive polymer. The improved properties, such as adhesion, should occur when the dispersion is subjected to potassium hydroxide and/or elevated temperatures. It is a further objective to provide a dispersion which may be utilized on the bipolar plates of a fuel cell or as a current collector of bipolar electrodes used in an ultracapacitor.
This invention relates to a graphite and/or carbon black-containing cathode coating dispersion which is suitable for battery production. The dispersion is water, acid and alkali resistant and also electrically conductive when coated on cathode surfaces. The dispersion is a water-based system which contains a binder which is an epoxy resin and is cured with an amine curative. The dispersion is maintained as a two-pot compound wherein the epoxy dispersion is mixed with an amine curative at the time of application. The epoxy resins are preferably a Bisphenol A or Bisphenol F Epichlorohydrin based epoxy or epoxy novalac.